The present invention relates to the field of general maintenance.
Many industrial, commercial, and household applications require the breaking up of relatively large objects into smaller pieces. In landscaping, for example, it is often useful to reduce uprooted trees and shrubs or their trimmings to wood chips, which are then used as mulch or hauled off as waste. In the farming industry, it may be useful to shred or grind feed, manure or other materials. In the construction industry, it may be necessary to reduce waste lumber and gypsum board to relatively small chips for disposal. In other applications, roots, newspapers, aluminum, plastic, discarded house plants, general rubbish, and other materials may have to be similarly reduced to smaller pieces.
The reduction process is variously referred to as cutting, chipping, shredding, mulching or grinding, depending in part on the size of the end product. Cutting and chipping is historically accomplished by a relatively few knives mounted directly onto a rotating disc, and produces pieces ranging up to about 3/4 to 11/2 inches in size. Shredding, mulching and grinding are historically accomplished by a dozen or more hammers which rotate about shafts attached to the disc. Such hammers typically operate within a chamber, and continue to reduce the size of the material being worked upon until that material can escape the chamber through a screen. Shredding generates pieces ranging from about 1/4 to about 3/4" in size, while mulching or grinding produces pieces ranging from a fine powder to about 1/4". Because of the overlap in the common usage of these terms, "cutting" and "chipping" are used interchangeably herein, and "shredding", "mulching" and "grinding" are used interchangeably herein. Additionally, all devices which perform any such reduction of materials are referred to herein by the generic name, chipper/mulcher.
In previous devices, the chipping knives are usually placed on the opposite side of the disc from the hammers. Such a configuration allows a user to either chip a material by forcing it against one side of the disc, or to mulch the material by forcing it into the chamber on the other side of the disc. One drawback to such an arrangement is that a given material cannot be chipped and mulched at the same time.
Also in the previous devices, the hammers comprise either independently pivoting plates with a long axis parallel to the direction of motion, or a row of teeth arranged along an edge of a single flat plate, and positioned normal to the direction of motion. (see U.S. Pat. No. 1,759,905). The present inventor recognized that both such configurations have several drawbacks which adversely affect performance and/or maintenance costs.
First, the hammers of both prior configurations strike the materials fed into the device with dull, flat surfaces. This may be useful for mulching and grinding, but offers relatively little assistance in cutting, chipping and shredding.
Second, the prior devices exhibit a poor trade-off with respect to maintenance costs. Independently pivoting flat plates are relatively strong along their striking axis, but are relatively thin from side to side. Because of these characteristics, individually pivoting flat plates tend to wear out at the pivot, and also tend to bend and twist about the supporting shaft. Such plates can be extremely difficult to remove and replace, at times requiring a blowtorch for their removal. Similarly, such plates tend to bend to such a degree that they cannot realistically be sharpened or reversed after removal. Turning the plate 90.degree. and cutting a row of teeth into the plate minimizes the twisting and bending about the supporting shaft, but such teeth are necessarily thin and weak because their thickness is limited by the thickness of the plate.